Method for receiving control information in a wireless communication system, and apparatus for same

ABSTRACT

The present invention discloses a method in which user equipment receives control information in a wireless communication system adopting carrier aggregation. In detail, the method comprises the steps of receiving a control region via one or more component carriers from among a plurality of component carriers transmitted by a base station, and performing a blind decoding process on the control region to obtain control information allocated to the user equipment, wherein the control region includes control information for said one or more component carriers or control information for the rest of the component carriers.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method for receiving control information in auser equipment of a wireless communication system to which a carrieraggregation scheme is applied and an apparatus for the same.

BACKGROUND ART

A 3^(rd) generation partnership project long term evolution (3GPP LTE),LTE-Advanced (hereinafter, referred to as ‘LTE-A’) communication systemwhich is an example of a mobile communication system to which thepresent invention can be applied will be described in brief.

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS) which is an exampleof a mobile communication system. The E-UMTS system is an evolvedversion of the conventional UMTS system, and its basic standardizationis in progress under the 3rd Generation Partnership Project (3GPP). TheE-UMTS may also be referred to as a Long Term Evolution (LTE) system.For details of the technical specifications of the UMTS and E-UMTS,refer to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE) 120, basestations (eNode B and eNB) 110 a and 110 b, and an Access Gateway (AG)which is located at an end of a network (E-UTRAN) and connected to anexternal network. Generally, the base stations can simultaneouslytransmit multiple data streams for a broadcast service, a multicastservice and/or a unicast service.

One or more cells may exist for one base station. One cell is set to oneof bandwidths of 1.25, 2.5, 5, 10, and 20 MHz to provide a downlink oruplink transport service to several user equipments. Different cells maybe set to provide different bandwidths. Also, one base station controlsdata transmission and reception for a plurality of user equipments. Thebase station transmits downlink (DL) scheduling information of downlinkdata to the corresponding user equipment to notify time and frequencydomains to which data will be transmitted and information related toencoding, data size, hybrid automatic repeat and request (HARQ). Also,the base station transmits uplink (UL) scheduling information of uplinkdata to the corresponding user equipment to notify time and frequencydomains that can be used by the corresponding user equipment, andinformation related to encoding, data size, HARQ. An interface fortransmitting user traffic or control traffic can be used between thebase stations. A Core Network (CN) may include the AG and a network nodeor the like for user registration of the UE. The AG manages mobility ofa UE on a Tracking Area (TA) basis, wherein one TA includes a pluralityof cells.

Although the wireless communication technology developed based on WCDMAhas been evolved into LTE, request and expectation of users andproviders have continued to increase. Also, since another wirelessaccess technology is being continuously developed, new evolution of thewireless communication technology is required for competitiveness in thefuture. In this respect, reduction of cost per bit, increase ofavailable service, use of adaptable frequency band, simple structure,open type interface, proper power consumption of user equipment, etc.are required.

Recently, standardization of advanced technology of LTE is in progressunder the 3rd Generation Partnership Project (3GPP). This technologywill be referred to as “LTE-Advanced” or “LTE-A.” One of importantdifferences between the LTE system and the LTE-A system is difference insystem bandwidth. The LTE-A system aims to support a wideband of maximum100 MHz. To this end, the LTE-A system uses carrier aggregation orbandwidth aggregation that achieves a wideband using a plurality ofcomponent carriers. For wider frequency bandwidth, the carrieraggregation aims to use a plurality of component carriers as one greatlogical frequency band. A bandwidth of each component carrier can bedefined based on a bandwidth of a system block used in the LTE system.Each component carrier is transmitted using a component carrier. In thisspecification, the component carrier may mean a component carrier forcarrier aggregation or a center carrier of the component carrierdepending on the context. The component carrier for carrier aggregationand the center carrier of the component carrier may be used together.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the conventionalproblem is to provide a method for receiving control information in auser equipment of a wireless communication system to which a carrieraggregation scheme is applied and an apparatus for the same.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat have been particularly described hereinabove and the above andother objects that the present invention could achieve will be moreclearly understood from the following detailed description.

Technical Solution

In an aspect of the present invention, a method for receiving controlinformation by a user equipment in a wireless communication system towhich a carrier aggregation scheme is applied comprises the steps ofreceiving a control region from a base station through one or more of aplurality of component carriers; and performing blind decoding for thecontrol region to acquire the control information allocated to the userequipment, wherein the control region includes control information onthe one or more component carriers or control information on the othercomponent carriers. Preferably, the method further comprises the step ofreceiving information on the one or more component carriers from thebase station before receiving the control region.

Also, the step of receiving control information includes performingblind decoding for the same search space corresponding to each of theone or more component carriers, and the control information is subjectedto channel coding of one codeword basis.

Moreover, the one or more component carriers are divided into componentcarriers for downlink control information and component carriers foruplink control information.

In another aspect of the present invention, a user equipment in awireless communication system to which a carrier aggregation scheme isapplied comprises a receiving module receiving a control region from abase station through one or more of a plurality of component carriers;and a processor performing blind decoding for the control region toacquire the control information allocated to the user equipment, whereinthe control region includes control information on the one or morecomponent carriers or control information on the other componentcarriers. Preferably, the receiving module receives information on theone or more component carriers from the base station.

Also, the processor performs blind decoding for the same search spacecorresponding to each of the one or more component carriers, and thecontrol information is subjected to channel coding of one codewordbasis.

Moreover, the one or more component carriers are divided into componentcarriers for downlink control information and component carriers foruplink control information.

Advantageous Effects

According to the embodiments of the present invention, in a wirelesscommunication system to which a carrier aggregation scheme is applied, auser equipment can effectively receive control information on componentcarriers from a base station.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS), which is an exampleof a mobile communication system;

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a user equipment andE-UTRAN based on the 3GPP radio access network standard;

FIG. 3 is a diagram illustrating physical channels used in a 3GPP systemand a general method for transmitting a signal using the physicalchannels;

FIG. 4 is a diagram illustrating a structure of a radio frame used in anLTE system;

FIG. 5 is a diagram illustrating a functional structure of a downlinkradio frame;

FIG. 6 is a diagram illustrating a resource grid of a downlink slot;

FIG. 7 is a diagram illustrating a control channel included in a controlregion of a subframe;

FIG. 8 is a diagram illustrating a resource unit used to constitute acontrol channel;

FIG. 9 is a diagram illustrating CCE distribution in a system band;

FIG. 10 is a conceptional diagram illustrating carrier aggregation;

FIG. 11 is a diagram illustrating an example of transmission of controlinformation through a plurality of component carriers in an LTE-Asystem;

FIG. 12 is a diagram illustrating another example of transmission ofcontrol information through a plurality of component carriers in anLTE-A system; and

FIG. 13 is a diagram illustrating a transmitter and a receiver, whichcan be applied to one embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, structures, operations, and other features of the presentinvention will be understood readily by the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to 3GPP system.

Hereinafter, a system that includes a system band of a single componentcarrier will be referred to as a legacy system or a narrowband system.By contrast, a system that includes a system band of a plurality ofcomponent carriers and uses at least one or more component carriers as asystem block of a legacy system will be referred to as an evolved systemor a wideband system. The component carrier used as a legacy systemblock has the same size as that of the system block of the legacysystem. On the other hand, there is no limitation in sizes of the othercomponent carriers. However, for system simplification, the sizes of theother component carriers may be determined based on the size of thesystem block of the legacy system. For example, the 3GPP LTE (Release-8)system and the 3GPP LTE-A (Release-9) system are evolved from the legacysystem.

Based on the aforementioned definition, the 3GPP LTE (Release-8) systemwill herein be referred to as an LTE system or the legacy system. Also,a user equipment that supports the LTE system will be referred to as anLTE user equipment or a legacy user equipment. The 3GPP LTE-A(Release-9) system will be referred to as an LTE-A system or an evolvedsystem. Also, a user equipment that supports the LTE-A system will bereferred to as an LTE-A user equipment or an evolved user equipment.

For convenience, although the embodiment of the present invention willbe described based on the LTE system and the LTE-A system in thisspecification, the LTE system and the LTE-A system are only exemplary,and the embodiment of the present invention can be applied to allcommunication systems corresponding to the aforementioned definition.Also, although the embodiment of the present invention will be describedbased on an FDD mode in this specification, the FDD mode is onlyexemplary, and the embodiment of the present invention can easily beapplied to an H-FDD mode or a TDD mode.

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a user equipment andE-UTRAN based on the 3GPP radio access network standard. The controlplane means a passageway where control messages are transmitted, whereinthe control messages are used in the user equipment and the network tomanage call. The user plane means a passageway where data generated inan application layer, for example, voice data or Internet packet dataare transmitted.

A physical layer as the first layer provides an information transferservice to an upper layer using a physical channel. The physical layer(PHY) is connected to a medium access control (MAC) layer via atransport channel, wherein the medium access control layer is locatedabove the physical layer. Data are transferred between the medium accesscontrol layer and the physical layer via the transport channel. Data aretransferred between one physical layer of a transmitting side and theother physical layer of a receiving side via the physical channel. Thephysical channel uses time and frequency as radio resources. In moredetail, the physical channel is modulated in accordance with anorthogonal frequency division multiple access (OFDMA) scheme in adownlink, and is modulated in accordance with a single carrier frequencydivision multiple access (SC-FDMA) scheme in an uplink.

A medium access control layer of the second layer provides a service toa radio link control (RLC) layer above the MAC layer via a logicalchannel. The RLC layer of the second layer supports reliable datatransfer. The RLC layer may be implemented as a functional block insidethe MAC layer. In order to effectively transmit data using IP packets(e.g., IPv4 or IPv6) within a radio interface having a narrow bandwidth,a packet data convergence protocol (PDCP) layer of the second layerperforms header compression to reduce the size of unnecessary controlinformation.

A radio resource control (hereinafter, abbreviated as ‘RRC’) layerlocated on a lowest part of the third layer is defined in the controlplane only. The RRC layer is associated with configuration,re-configuration and release of radio bearers (hereinafter, abbreviatedas ‘RBs’) to be in charge of controlling the logical, transport andphysical channels. In this case, the RB means a service provided by thesecond layer for the data transfer between the user equipment and thenetwork. To this end, the RRC layer of the user equipment and thenetwork exchanges RRC message with each other. If the RRC layer of theuser equipment is RRC connected with the RRC layer of the network, theuser equipment is in RRC connected mode. If not so, the user equipmentis in RRC idle mode. A non-access stratum (NAS) layer located above theRRC layer performs functions such as session management and mobilitymanagement.

One cell constituting eNB is established at one of bandwidths of 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to several user equipments. At this time, differentcells may be established to provide different bandwidths.

As downlink transport channels carrying data from the network to theuser equipment, there are provided a broadcast channel (BCH) carryingsystem information, a paging channel (PCH) carrying paging message, anda downlink shared channel (SCH) carrying user traffic or controlmessages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted via the downlink SCH or anadditional downlink multicast channel (MCH). Meanwhile, as uplinktransport channels carrying data from the user equipment to the network,there are provided a random access channel (RACH) carrying an initialcontrol message and an uplink shared channel (UL-SCH) carrying usertraffic or control message. As logical channels located above thetransport channels and mapped with the transport channels, there areprovided a broadcast control channel (BCCH), a paging control channel(PCCH), a common control channel (CCCH), a multicast control channel(MCCH), and a multicast traffic channel (MTCH).

FIG. 3 is a diagram illustrating physical channels used in a 3GPP systemand a general method for transmitting a signal using the physicalchannels.

The user equipment performs initial cell search such as synchronizingwith the base station when it newly enters a cell or the power is turnedon (S301). To this end, the user equipment synchronizes with the basestation by receiving a primary synchronization channel (P-SCH) and asecondary synchronization channel (S-SCH) from the base station, andacquires information of cell ID, etc. Afterwards, the user equipment mayacquire broadcast information within the cell by receiving a physicalbroadcast channel (PBCH) from the base station. In the mean time, theuser equipment may identify the status of a downlink channel byreceiving a downlink reference signal (DL RS) in the initial cell searchstep.

The user equipment which has finished the initial cell search mayacquire more detailed system information by receiving a physicaldownlink shared channel (PDSCH) in accordance with a physical downlinkcontrol channel (PDCCH) and information carried in the PDCCH (S302).

In the mean time, if the user equipment initially accesses the basestation, or if there is no radio resource for signal transmission, theuser equipment performs a random access procedure (RACH) for the basestation (S303 to S306). To this end, the user equipment may transmit apreamble of a specific sequence through a physical random access channel(PRACH) (S303 and S305), and may receive a response message to thepreamble through the PDCCH and the PDSCH corresponding to the PDCCH(S304 and S306). In case of a contention based RACH, a contentionresolution procedure may be performed additionally.

The user equipment which has performed the aforementioned steps mayreceive the PDCCH/PDSCH (S307) and transmit a physical uplink sharedchannel (PUSCH) and a physical uplink control channel (PUCCH) (S308), asa general procedure of transmitting uplink/downlink signals. Controlinformation transmitted from the user equipment to the base station orreceived from the base station to the user equipment through the uplinkincludes downlink/uplink ACK/NACK signals, a channel quality indicator(CQI), a precoding matrix index (PMI), a scheduling request (SR), and arank indicator (RI). In case of the 3GPP LTE system, the user equipmentmay transmit the aforementioned control information such as CQI/PMI/RIthrough the PUSCH and/or the PUCCH.

FIG. 4 is a diagram illustrating a structure of a radio frame used in anLTE system.

Referring to FIG. 4, the radio frame has a length of 10 ms(327200·T_(s)) and includes ten (10) subframes of an equal size. Eachsub frame has a length of 1 ms and includes two slots. Each slot has alength of 0.5 ms (15360·T_(s)). In this case, T_(s) represents asampling time, and is expressed by T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸(about 33 ns). The slot includes a plurality ofOFDM symbols in a time domain, and includes a plurality of resourceblocks (RBs) in a frequency domain. In the LTE system, one resourceblock includes twelve (12) subcarriers×seven (or six) OFDM symbols. Atransmission time interval (TTI), which is a transmission unit time ofdata, may be determined in a unit of one or more subframes. Theaforementioned structure of the radio frame is only exemplary, andvarious modifications may be made in the number of subframes included inthe radio frame or the number of slots included in the subframe, or thenumber of OFDM symbols included in the slot.

FIG. 5 is a diagram illustrating a functional structure of a downlinkradio frame.

Referring to FIG. 5, the downlink radio frame includes ten subframeshaving an equal length. In the 3GPP LTE system, the subframes aredefined in a basic time unit of packet scheduling for all downlinkfrequencies. Each subframe is divided into a control region fortransmission of scheduling information and other control channel and adata region for transmission of downlink data. The control region startsfrom the first OFDM symbol of the subframes and includes one or moreOFDM symbols. The control region may have a size set independently persubframe. The control region is used to transmit L1/L2 (layer 1/layer 2)control signals. The data region is used to transmit downlink traffic.

FIG. 6 is a diagram illustrating a resource grid of a downlink slot.

Referring to FIG. 6, the downlink slot includes N_(symb) ^(DL) number ofOFDM symbols in a time region and N_(RB) ^(DL) number of resource blocksin a frequency region. Since each resource block includes N_(se) ^(RB)number of subcarriers, the downlink slot includes N_(RB) ^(DL)×N_(se)^(RB) number of subcarriers in the frequency region. Although an exampleof FIG. 6 illustrates that the downlink slot includes seven OFDM symbolsand the resource block includes twelve subcarriers, the presentinvention is not limited to the example of FIG. 6. For example, thenumber of OFDM symbols included in the downlink slot may be varieddepending on a length of cyclic prefix (CP).

Each element on the resource grid will be referred to as a resourceelement (RE). One resource element is indicated by one OFDM symbol indexand one subcarrier index. One resource block (RB) includes N_(symb)^(DL)×N_(se) ^(RB) number of resource elements. The number N_(RB) ^(DL)of resource blocks included in the downlink is subjected to a downlinktransmission bandwidth established in a cell.

FIG. 7 is a diagram illustrating a control channel included in a controlregion of a subframe.

Referring to FIG. 7, the subframe includes fourteen (14) OFDM symbols.First one to three OFDM symbols are used as the control region inaccordance with establishment of subframe, and the other thirteen toeleven OFDM symbols are used as the data region.

In FIG. 7, R1 to R4 represent reference signals (RS) of antennas 0 to 3.The RS is fixed by a given pattern within the subframe regardless of thecontrol region and the data region. The control channel is allocated toa resource to which the RS is not allocated in the control region, andthe traffic channel is also allocated to a resource to which the RS isnot allocated in the data region. Examples of the control channelallocated to the control region include PCFICH (Physical Control FormatIndicator CHannel), PHICH (Physical Hybrid-ARQ Indicator CHannel), andPDCCH (Physical Downlink Control CHannel).

The PCFICH notifies the user equipment of the number of OFDM symbolsused in the PDCCH per subframe. The PCFICH is located in the first OFDMsymbol and established prior to the PHICH and the PDCCH. The PCFICHincludes four resource element groups (REG), each of which isdistributed in the control region based on cell ID. One REG includesfour REs. The structure of the REG will be described in detail withreference to FIG. 8. The PCFICH value indicates values of 1 to 3, and ismodulated by Quadrature Phase Shift Keying (QPSK).

The PHICH is used to transmit HARQ ACK/NACK signals for uplinktransmission. The PHICH includes three REGs, and is cell-specificallyscrambled. The ACK/NACK signals are indicated by 1 bit, and are spreadby a spreading factor (SF)=2 or 4, wherein spreading is repeated threetimes. A plurality of PHICHs may be mapped with the same resource. ThePHICH is modulated by Binary Phase Shift Keying (BPSK).

The PDCCH is allocated to first n number of OFDM symbols of thesubframe, wherein n is an integer greater than 1 and is indicated by thePCIFCH. The PDCCH includes one or more CCEs, which will be described indetail later. The PDCCH notifies each user equipment or user equipmentgroup of information related to resource allocation of transportchannels, i.e., a paging channel (PCH) and a downlink-shared channel(DL-SCH), uplink scheduling grant, HARQ information, etc.

The PCH and the DL-SCH are transmitted through the PDSCH. Accordingly,the base station and the user equipment respectively transmit andreceive data through the PDSCH except for specific control informationor specific service data.

Information as to user equipment(s) (one user equipment or a pluralityof user equipments) to which data of the PDSCH are transmitted, andinformation as to how the user equipment(s) receives and decodes PDSCHdata are transmitted through the PDCCH. For example, it is assumed thata specific PDCCH is CRC masked with radio network temporary identity(RNTI) called “A,” and information on data transmitted using a radioresource (for example, frequency location) called “B” and transmissionformat information (for example, transport block size, modulation mode,coding information, etc.) called “C” is transmitted through a specificsubframe. In this case, one or more user equipments located in acorresponding cell monitor the PDCCH using their RNTI information, andif there are one or more user equipments having RNTI “A”, the userequipments receive the PDCCH and receive the PDSCH indicated by “B” and“C” through information of the received PDCCH.

FIG. 8( a) and FIG. 8( b) illustrate resource units used to configure acontrol channel. In particular, FIG. 8( a) illustrates that the numberof transmitting antennas belonging to the base station is 1 or 2, andFIG. 8( b) illustrates that the number of transmitting antennasbelonging to the base station is 4. In FIG. 8( a) and FIG. 8( b),different reference signal patterns are illustrated depending on thenumber of transmitting antennas but a method of establishing a resourceunit related to a control channel is illustrated equally.

Referring to FIG. 8( a) and FIG. 8( b), a basic resource unit of thecontrol channel is REG. The REG includes four neighboring resourceelements excluding the reference signals. The REG is illustrated with asolid line. The PCFIC and the PHICH include four REGs and three REGs,respectively. The PDCCH is configured in a unit of CCE (control channelelement), one CCE including nine REGs.

The user equipment is established to identify M(L)(≧L) number of CCEsarranged continuously or arranged by a specific rule, whereby the userequipment may identify whether the PDCCH of L number of CCEs istransmitted thereto. A plurality of L values may be considered by theuser equipment to receive the PDCCH. CCE sets to be identified by theuser equipment to receive the PDCCH will be referred to as a searchspace. For example, the LTE system defines the search space as expressedin Table 1.

TABLE 1 Number of Search space S_(k) ^((L)) PDCCH Aggregation Sizecandidates Type level L [in CCEs] M^((L)) DCI formats UE- 1 6 6 0, 1,1A, specific 2 12 6 1B, 2 4 8 2 8 16 2 Common 4 16 4 0, 1A, 1C, 8 16 23/3A

In this case, CCE aggregation level L represents the number of CCEsconstituting the PDCCH, S_(k) ^((L)) represents a search space of theCCE aggregation level L, and M^((L)) represents the number of PDCCHcandidates to be monitored in the search space.

The search space may be divided into a UE-specific search space thatallows access to only a specific user equipment and a common searchspace that allows access to all user equipments within a cell. The userequipment monitors a common search space of the CCE aggregation levelsof L=4 and L=8, and monitors a UE-specific search space of the CCEaggregation levels of L=1, L=2, L=4 and L=8. The common search space andthe UE-specific search space may be overlapped with each other.

Furthermore, in the PDCCH search space given to a random user equipmentfor each CCE aggregation level value, the location of the first CCE(i.e., CCE having the smallest index) is varied per subframe dependingon the user equipment. This will be referred to as a PDCCH search spacehashing.

FIG. 9 is a diagram illustrating an example of a control channel element(CCE) distributed into a system band. Referring to FIG. 9, a pluralityof logically continuous CCEs are input to an interleaver. Theinterleaver performs interleaving of the plurality of CCEs in a unit ofREG. Accordingly, the frequency/time resources constituting one CCE arephysically distributed into all frequency/time regions within thecontrol region of the subframe. As a result, although the controlchannel is configured in a unit of CCE, since interleaving is performedin a unit of REG, frequency diversity and interference randomizationgain can be maximized.

FIG. 10 is a conceptional diagram illustrating carrier aggregation. Thecarrier aggregation means that a plurality of component carriers areused as a huge logical frequency band so that the wireless communicationsystem uses a wider frequency band.

Referring to FIG. 10, all system bandwidths (BW) are logical bandwidthsand have a maximum bandwidth of 100 MHz. The system bandwidths includefive component carriers, each of which has a maximum bandwidth of 20MHz. The basic component carrier includes one or more physicallycontinuous subcarriers. Although the respective component carriers havethe same bandwidth in FIG. 10, this is only exemplary and the componentcarriers may have different bandwidths. Also, although it is illustratedthat the respective component carriers adjoin each other in thefrequency region, this illustration is logically exemplary and therespective component carriers may physically adjoin each other or may bespaced apart from each other.

Center carriers may be used differently for the respective componentcarriers, or one common center carrier may be used for physicallyadjoined component carriers. For example, if it is assumed that allcomponent carriers physically adjoin one another in FIG. 10, centercarrier A may be used. Also, if it is assumed that the respectivecomponent carriers do not adjoin physically one another in FIG. 10,center carrier A and center carrier B may be used separately for thecomponent carriers.

In this specification, the component carrier may correspond to thesystem band of the legacy system. As the component carrier is definedbased on the legacy system, it is possible to facilitate backwardcompatibility and system design in a radio communication environmentwhere an evolved user equipment and a legacy user equipment coexist. Forexample, if the LTE-A system supports carrier aggregation, therespective component carrier may correspond to the system band of theLTE system. In this case, the bandwidth of each component carrier mayhave any one of 1.25, 2.5, 5, 10, and 20 MHz.

If the whole system bandwidth is extended to carrier aggregation, thefrequency bandwidth used for communication of user equipments is definedin a unit of component carrier. User equipment A may use 100 MHz whichcorresponds to the whole system bandwidth, and performs communicationusing all of five component carriers. User equipments B₁ to B₅ may useonly a bandwidth of 20 MHz and perform communication using one componentcarrier. User equipments C₁ and C₂ may use a bandwidth of 40 MHz andperform communication using two component carriers. The two componentcarriers may or may not logically/physically adjoin each other. The userequipment C₁ represents that two component carriers which do not adjoineach other are used, the user equipment C₂ represents that two componentcarriers which adjoin each other are used.

In the mean time, in the current LTE system, the user equipment shouldperform blind decoding of maximum 44 times to detect the PDCCHtransmitted from the base station to the user equipment and acquiredownlink control information (DCI) included in the PDCCH. However, inthe LTE-A system to which carrier aggregation is applied, since datatransmission and reception is performed through a plurality of componentcarriers, the base station should transmit DCI, i.e., schedulinginformation on a plurality of uplink component carriers and a pluralityof downlink component carriers, and the user equipment should acquirethe PDCCH allocated thereto through blind decoding, wherein the PDCCHexists in a control region of the plurality of component carriers.

FIG. 11 is a diagram illustrating an example of transmission of controlinformation through a plurality of component carriers in an LTE-Asystem.

Referring to FIG. 11, the base station allocates control information oneach component carrier to a control region of a corresponding componentcarrier in accordance with a current DCI format. Also, the userequipment should acquire scheduling information on each componentcarrier, i.e., DCI received through PDCCH by performing blind decodingfor each component carrier. Accordingly, decoding complexity foracquiring DCI on all the component carriers may be increased inproportion to the number of component carriers.

For example, it is assumed that a total number of blind decoding timesof the user equipment is N times, the size of the user equipmentspecific search space is Mu and the size of the common search space isMc. Also, if blind decoding at the user equipment specific search spaceis performed Nu times and blind decoding at the common search space isperformed Nc times, a total number of blind decoding times per componentcarrier will be Mu*Nu+Mc*Nc times. At this time, if the number ofcomponent carriers is C and a carrier aggregation scheme is used, atotal number of blind decoding times will be C*(Mu*Nu+Mc*Nc) times asfar as there is no specific method for reducing blind decodingcomplexity. Accordingly, if C*(Mu*Nu+Mc*Nc) is greater than the totalnumber of blind decoding times N of the user equipment, it means thatthe user equipment may end blind decoding without searching for thePDCCH transmitted from the base station.

FIG. 12 is a diagram illustrating another example of transmission ofcontrol information through a plurality of component carriers in anLTE-A system.

Referring to FIG. 12, a blind decoding parameter of another componentcarrier is transmitted from a specific component carrier, i.e., anchorcarrier or primary carrier, whereby blind decoding complexity may bereduced. However, in this case, if decoding of the specific componentcarrier is failed, a problem occurs in view of reliability in thatdecoding of the other component carriers may be failed.

Hereinafter, in the LTE-A system to which a carrier aggregation schemeis applied, if the base station allocates control information on eachcomponent carrier to the control region of the corresponding componentcarrier, methods for reducing blind decoding complexity performed by theuser equipment to acquire PDCCH allocated to the user equipment aresuggested as follows.

1) Reduction of the Number of Component Carriers to be Searched

If the user equipment reduces the number of component carriers to besearched, so as to acquire control information, it means that one ormore of all the component carriers allocated to the user equipmentinclude control information of the other component carriers.Accordingly, the number of blind decoding times and the size of thesearch space corresponding to the number of blind decoding times may bedefined per component carrier, whereby a total number of blind decodingtimes may be N times. In this case, it is noted that control informationon the other component carriers does not mean a decoding parameter ofthe other component carriers.

In the mean time, the user equipment may be set to search for the PDCCHat the same search space per component carrier, whereby a total numberof blind decoding times may be less than N times.

However, information as to which component carrier includes schedulinginformation, i.e., information as to reduction of the number ofcomponent carriers to be searched should previously be shared betweenthe base station and the user equipment, and this signaling may beperformed through an upper layer.

2) Size of Search Space

The size of the search space for one component carrier may be increasedor reduced. In other words, if blind decoding performance of the userequipment is not sufficient to perform decoding for all the componentcarriers allocated to the user equipment, the size of the search spacemay be reduced. Also, if blind decoding performance of the userequipment is sufficient to perform decoding for all the componentcarriers allocated to the user equipment, the size of the search spacemay be increased.

First of all, if the size of the search space is reduced, a new searchspace different from the search space of the LTE system according to therelated art may be defined and the number of search spaces may berestricted in accordance with a CCE aggregation level. In other words,if the new search space is defined, a specific CCE aggregation levelapplied to the new search space or a group of CCE aggregation levels maybe defined. For example, if one CCE aggregation level is used and tenuser equipment specific search spaces per component carrier are defined,the search spaces may be defined as ten continuous logical search spacesstarting from the user equipment specific search space dependent uponsubframe index. Also, if two CCE aggregation levels are defined, tenuser equipment specific search spaces per component carrier may equallybe divided into two groups. In this case, each CCE aggregation level maycorrespond to five search spaces having the same start point as that ofthe existing user equipment specific search space. In the mean time, ifa search space structure applied to the existing LTE system ismaintained, reduction in the size of the search space may be implementedsimply by reduction of the number of search spaces per CCE aggregationlevel. For example, the search space corresponding to the smallest CCEaggregation level or the greatest CCE aggregation level may be removedto reduce the size of the search space.

On the other hand, if the size of the search space is increased, thenumber of search spaces according to the existing LTE system may beadded to correspond to the smallest CCE aggregation level or thegreatest CCE aggregation level, or the search spaces corresponding tothe respective CCE aggregation levels may be added as much as therespective CCE aggregation levels. Also, the search spaces correspondingto the respective CCE aggregation levels may be added in proportion tothe size of the existing search space.

As described above, even in the case that the new search space isdefined, information on the added search space should be shared inadvance between the base station and the user equipment, and thissignaling may be performed through an upper layer.

3) The Number of Decoding Times Per Search Space

Under the assumption that there is no big change in a transmission modeas actual transmission is performed, the number of blind decoding timesper search space may be restricted. In more detail, a downlink PDCCHindication structure may be the same as an uplink PDCCH indicationstructure regardless of the transmission mode. In this case, although aDCI format of a downlink grant may be different from that of an uplinkgrant, bits for channel coding may be set equally regardless of adownlink or an uplink. In other words, padding bits may be added to adownlink DCI format of a short length or a DCI format of an uplink grantto constitute one codeword length. Accordingly, since the user equipmentcan detect two uplink and downlink DCI formats by decoding one codeword,the number of blind decoding times may be reduced to half.

It will be apparent to the person with ordinary skill in the art towhich the present invention pertains that the aforementioned threeparameters may be used independently or in combination.

In the mean time, the aforementioned three parameters may be useddifferently in accordance with uplink scheduling and downlinkscheduling. Since scheduling information on a downlink component carriermay generally be more than that on a downlink component carrier,scheduling for an uplink component carrier may be indicated differentlyfrom scheduling for a downlink component carrier.

For example, it is assumed that downlink scheduling informationcorresponds to five downlink component carriers and uplink schedulinginformation corresponds to two uplink component carriers. In this case,if one PDCCH includes only scheduling information on one componentcarrier, a total number of uplink PDCCHs will be two. If the number ofuplink PDCCHs is restricted as above, the other component carriers maybe used to decode downlink scheduling information only. Also, if aprimary component carrier for scheduling exists, a primary componentcarrier for uplink scheduling and a primary component carrier fordownlink scheduling may be set separately.

As described above, if a primary component carrier for uplink schedulingand a primary component carrier for downlink scheduling existseparately, the base station may previously notify the user equipment ofDCI grant information on a component carrier to be searched from acontrol region of the primary component carrier for downlink scheduling.In other words, the user equipment may previously identify schedulinginformation on component carrier(s) to be searched, from a specificdownlink component carrier. This information may be indicated from thebase station to the user equipment through upper layer signaling.

FIG. 13 is a diagram illustrating a communication transceiver accordingto the embodiment of the present invention. The transceiver may be apart of the base station and the user equipment.

Referring to FIG. 13, the transceiver 1300 includes a processor 1310, amemory 1320, a radio frequency (RF) module 1330, a display module 1340,and a user interface module 1350. The transceiver 1300 is illustratedfor convenience of description, and some of its modules may be omitted.Also, the transceiver 1300 may further include necessary modules.Moreover, some modules of the transceiver 1300 may be divided intosegmented modules. The processor 1310 is configured to perform theoperation according to the embodiment of the present inventionillustrated with reference to the drawings. If the transceiver 1300 is apart of the base station, the processor 1310 may generate a controlsignal and map the control signal into a control channel configuredwithin a plurality of component carriers. In more detail, the processor1310 of the transceiver 1300 which is a part of the base station may mapcontrol information through one or more of a plurality of componentcarriers to reduce blind decoding complexity of the user equipment. Inthis case, the number of blind decoding times and the size of the searchspace corresponding to the number of blind decoding times may be definedper component carrier, whereby the total number of blind decoding timesmay be N times. In this case, it is noted that control information onthe other component carriers does not mean a decoding parameter of theother component carriers. The processor 1310 of the transceiver 1300which is a part of the base station may constitute one codeword lengthby adding padding bits to a DCI format of a downlink grant and a DCIformat of an uplink grant. Accordingly, since the user equipment candetect two uplink and downlink DCI formats by decoding one codeword, thenumber of blind decoding times may be reduced.

Also, if the transceiver 1300 is a part of the user equipment, theprocessor 1310 may identify the control channel indicated by a signalreceived from the plurality of component carriers and extract thecontrol signal from the control channel. Afterwards, the processor 1310may perform the operation required based on the control signal. In moredetail, the processor 1310 of the transceiver 1300 which is a part ofthe user equipment searches for PDCCH at the same search space percomponent carrier to perform blind decoding, whereby a total number ofblind decoding times may be less than N times. Also, if blindperformance of the user equipment is not sufficient to perform blinddecoding for all the component carriers allocated to the user equipment,the processor 1310 may reduce the size of the search space. By contrast,if blind performance of the user equipment is sufficient to performblind decoding for all the component carriers allocated to the userequipment, the processor 1310 may increase the size of the search space.Also, if the processor 1310 of the transceiver 1300 which is a part ofthe user equipment may constitute one codeword length by adding paddingbits to a DCI format of a downlink grant and a DCI format of an uplinkgrant, since the user equipment can detect two uplink and downlink DCIformats by decoding one codeword, the number of blind decoding times maybe reduced to half.

The memory 1320 is connected with the processor 1310 and stores anoperating system, an application, a program code, and data therein. TheRF module 1330 is connected with the processor 1310 and converts abaseband signal to a radio signal or vice versa. To this end, the RFmodule 1330 performs analog conversion, amplification, filtering andfrequency uplink conversion, or their reverse processes. The displaymodule 1340 is connected with the processor 1310 and displays variouskinds of information. Examples of the display module 1340 include, butnot limited to, a liquid crystal display (LCD), a light emitting diode(LED), and an organic light emitting diode (OLED). The user interfacemodule 1350 is connected with the processor 1310, and can be configuredby combination of well known user interfaces such as keypad and touchscreen.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined type.Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with another claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

The embodiments of the present invention have been described based onthe data transmission and reception between the base station and theuser equipment. A specific operation which has been described as beingperformed by the base station may be performed by an upper node of thebase station as the case may be. In other words, it will be apparentthat various operations performed for communication with the userequipment in the network which includes a plurality of network nodesalong with the base station can be performed by the base station ornetwork nodes other than the base station. The base station may bereplaced with terms such as a fixed station, Node B, eNode B (eNB), andaccess point. Also, the user equipment may be replaced with terms suchas mobile station (MS) and mobile subscriber station (MSS).

The embodiments according to the present invention may be implemented byvarious means, for example, hardware, firmware, software, or theircombination. If the embodiment according to the present invention isimplemented by hardware, the embodiment of the present invention can beimplemented by one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, microcontrollers,microprocessors, etc.

If the embodiment according to the present invention is implemented byfirmware or software, the embodiment of the present invention may beimplemented by a type of a module, a procedure, or a function, whichperforms functions or operations described as above. A software code maybe stored in a memory unit and then may be driven by a processor. Thememory unit may be located inside or outside the processor to transmitand receive data to and from the processor through various means whichare well known.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a wireless communication system.More specifically, the present invention may be applied to a method forreceiving control information in a user equipment of a wirelesscommunication system to which carrier aggregation is applied.

1. A method for receiving control information by a user equipment in awireless communication system to which a carrier aggregation scheme isapplied, the method comprising the steps of: receiving a control regionfrom a base station through one or more of a plurality of componentcarriers; and performing blind decoding for the control region toacquire the control information allocated to the user equipment, whereinthe control region includes control information on the one or morecomponent carriers or control information on the other componentcarriers.
 2. The method according to claim 1, further comprising thestep of receiving information on the one or more component carriers fromthe base station before receiving the control region.
 3. The methodaccording to claim 1, wherein the step of receiving control informationincludes performing blind decoding for the same search spacecorresponding to each of the one or more component carriers.
 4. Themethod according to claim 1, wherein the control information issubjected to channel coding of one codeword basis.
 5. The methodaccording to claim 1, wherein the one or more component carriers aredivided into component carriers for downlink control information andcomponent carriers for uplink control information.
 6. A user equipmentin a wireless communication system to which a carrier aggregation schemeis applied, the user equipment comprising: a receiving module receivinga control region from a base station through one or more of a pluralityof component carriers; and a processor performing blind decoding for thecontrol region to acquire the control information allocated to the userequipment, wherein the control region includes control information onthe one or more component carriers or control information on the othercomponent carriers.
 7. The user equipment according to claim 6, whereinthe receiving module receives information on the one or more componentcarriers from the base station.
 8. The user equipment according to claim6, wherein the processor performs blind decoding for the same searchspace corresponding to each of the one or more component carriers. 9.The user equipment according to claim 6, wherein the control informationis subjected to channel coding of one codeword basis.
 10. The userequipment according to claim 6, wherein the one or more componentcarriers are divided into component carriers for downlink controlinformation and component carriers for uplink control information.